After a Chinese restaurant in Rome is threatened by the mafia, who will stop at nothing to acquire the property, the owner recruits a family friend in Hong Kong, kung fu expert Tang Lung, to help them defend their business.

One day, a shrimp fisherman catches a large tadpole. Dr. Yano discovers that the captured animal is not a tadpole, but a life form that originated in some chemical way in the polluted water of the bay. During experiments, the tadpole grows very rapidly and escapes, returning to the polluted water of the bay and growing into a monster. There happens to be another monster in the bay: Godzilla, in which the tadpole Hedra engages in a fight with.

A professor takes up a new post at an all-girls school only to discover the principal concealing a dark secret.

Dr. Nishiyama has to combat increasingly bizarre events on which seem all too familiar to the French prophet Nostradamus's predictions.

Through an experiment by Dr. Stewart with animal cells, a monster is created that is given the name Frankenstein. He is a gentle giant, but he escapes his guards and was supposedly killed on a mountain. After several years, a ship off the coast is attacked by a green monster, where the people think of Frankenstein. The green monster attacks the fortified country, in which the army is then called in for help. When a brown monster suddenly appears, Dr. Stewart understands that his Frankenstein was not killed, but has reproduced.

Thousands of years ago, Mechagodzilla, a robotic monster, was driven into the sea by Godzilla, Earth's defender. Recently, a submarine was dispatched to locate Mechagodzilla's remains. Overpowered by humans from the Third Planet, the scholar Dr. Mafune is forced to control two monsters through experiments and inventions in order to conquer Earth. However, when Mechagodzilla is ordered to destroy a ship, a fierce battle ensues.